The effect of humidity on gas sensing with ion mobility spectrometry

• We studied the accuracy of ion mobility measurements in dependence on humidity.
• The peak positions of product ions are unaffected by the humidity of sampling gas.
• The signal intensities of amines are constant over a humidity range up to 2000 ppm.
• Decreasing intensities are observable for toluenes and chlorinated compounds.
• The different product ion peaks of ketones show a different behavior.

Vaporized water molecules are unavoidable present in the ambient atmosphere and can considerably affect the analytical signals obtained with sensor techniques during real-time field measurements. Also the introduction of humidity into stand-alone ion mobility spectrometers cannot completely be avoided and the water vapor is transported via the carrier gas into spectrometer. For this case, we systematically investigated the way in which ion mobility measurements in positive mode are influenced. The drift times obtained with humid carrier gas are the same as those detected under dry conditions. They are constant over a range of water concentrations up to 2000 ppm. The nature of ions formed during the atmospheric chemical ionization processes is therefore independent on the humidity. However, the relative abundance of product ions can strongly be affected depending on the properties of substances investigated. While the signal intensity obtained for amines is comparatively unaffected by humidity, a significant decrease is observable for toluenes, chlorinated compounds and ketones.

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